1. Field of the Invention
This invention relates to thermoelectric devices for thermal management of microprocessor and other high power density chips.
2. Background of the Invention
A thermoelectric device can produce electrical energy when heat flows through opposite conductivity types of a thermoelectric material. Further, a thermoelectric device can cool an attached object when a current is flown in an appropriate direction through the thermoelectric material. Due to increases in the dimensionless thermoelectric figure of merit (ZT) in thermoelectric materials, both cooling and power conversion applications are possible with emerging thermoelectric technologies, such as for example the technologies described in the above-noted related applications.
One area attractive for thermoelectric application is in thermal management of integrated circuit chips. Advances in integrated circuit technology have led to faster clock frequencies and greater densities of transistors. These advances have resulted in a corresponding increase in the amount of heat generated by the integrated circuits (ICs). With large amounts of heat being generated, the problem of efficient heat dissipation has become more acute. Further, the increased density of chips produces problems due to local heating and thermally induced stress which can deteriorate chip performance and longevity. Also, cooling of transistor devices can lead to reduction of leakage currents, commonly referred to as Ioff in a CMOS device, which can in turn reduce the power consumed. In addition to heating problems with high-density circuits, supplying power to the enormous number of devices as well as power management are also becoming major issues. Thus, cooling with high-performance TE technology can potentially solve both the thermal management as well as power management problems.
A thermoelectric cooler can address these issues, for example, by removing heat from regions in the die (i.e., a medium) where heat dissipation is the highest. The thermoelectric device can be seen as a cooling device in which the cooling medium consists of electrons being electrically directed from the regions of heat generation to more remote regions where the heat contained in the electrons is dissipated. One advantage of a thermoelectric cooler in this application is that it does not require that fluids, such as for example as would be required with a heat pipe or a freon cooler, be integrated into the chip platform. Further, a thermoelectric device pumps heat to a region where more effective “passive” dissipation of heat into the environment around the chip platform is possible. More specifically, the heat is pumped to the hot side of the thermoelectric device which is in more intimate contact with the heat dissipating medium than the original heat generating region. Indeed, it is well known that passive cooling devices have a limited capacity to dissipate heat unless the passive cooling devices use microchannels which in turn require high fluid pressures
Thermoelectric coolers have been used to lower the operating temperature of semiconductor devices such as lasers. Conventionally, TE coolers have been developed separately from the integrated circuit device. The importance of developing TE coolers for semiconductor devices is evidenced by the extensive technological development directed to the subject, as seen in recent patent literature. U.S. Pat. No. 4,238,759, the entire contents of which are incorporated herein by reference, describes a Peltier device that cools an adjacent P-N junction. The Peltier junction is located a few microns from the lasing junction in this device. U.S. Pat. No. 4,279,292, the entire contents of which are incorporated herein by reference, describes a TE cooler in contact with a thermal heat sink that is in turn thermally connected to a charge coupled device. U.S. Pat. No. 5,012,325, the entire contents of which are incorporated herein by reference, describes a TE IC package in which the metalllizations of the IC constitute Peltier coolers. U.S. Pat. No. 5,362,983, the entire contents of which are incorporated herein by reference, describes a TE cooling module formed with ceramic substrate supports for the TE elements. U.S. Pat. No. 5,419,780, the entire contents of which are incorporated herein by reference, describes a Peltier cooler directly contacting an IC that is connected to a heat sink having a fan for additional cooling.
Yet, these approaches are limited in their performance due to the thermoelectric material characteristics of the thermoelements in the TE devices by the profile of the devices such that the thermoelectric devices provided only limited cooling power densities (such as 1 to 2 W/cm2) compared to the present invention which can provide cooling power densities in the range of 10 to 1000 W/cm2, by the system design which attempted to adapt a macroscopic TE technology to cool microscopic IC devices, or by the lack of the HAF-LIOF concepts that were discussed in the U.S. Provisional Application No. 60/528,479.